The two principal means for utilizing iron-ore fines for use in a blast furnace are by sintering or pelletizing. The preferred use of either method is normally dictated by location and the type of ore available. However, blast furnaces using a high percentage of ore pellets, greater than 80 percent, can have drawbacks attributable to the physical characteristics of the pellets. Namely, more pellets will roll toward the center of the blast furnace because of their spherical shape than will coke which has an irregular shape. The concentration of higher quantities of pellets in the center of the furnace results in higher quantities of coke at the wall and leads to two primary disadvantages in the operation of a blast furnace. The nonuniform packing of burden materials results in high reducing gas flows near the wall of the furnace which in turn results in (1) a decrease in furnace efficiency, i.e. lower productivity and higher coke rates, and (2) an increase in the rate of furnace lining erosion with associated increasing heat losses which result in a decrease in furnace campaign life. For example, the campaign life of a blast furnace for iron ore pellets is often about 2 years under these conditions. In addition to very high cost of relining the furnace, there is the costly shutdown time, often 2 to 3 months while this relining takes place.
One method to eliminate the deleterious results from the physical characteristics of pellets was disclosed in U.S. Pat. No. 4, 129,437, incorporated herein by reference, which presents a method for producing larger sized pellets and then crushing them to eliminate the spherical shape and increase surface area. This will increase the angle of repose of the crushed pellets over spherical pellets to approach that of sinter and coke. This results in more uniform distribution of burden materials. However, this method has the significant drawback of requiring the construction of large new crushing and screening facilities. There are also problems associated with the production of large size, good quality pellets suitable for making the crushed pellets.